1. Field of the Invention
The present invention relates to a liquid ejection head, an image forming apparatus, and a liquid ejection head manufacturing method, and more particularly to a liquid ejection head in which ejection ports for ejecting a liquid are disposed at a high density, an image forming apparatus, and a liquid ejection head manufacturing method.
2. Description of the Related Art
An inkjet printer (inkjet recording apparatus) having an inkjet head (liquid ejection head) in which a large number of nozzles (ejection ports) are arranged is known as an image forming apparatus. This inkjet printer records an image on a recording medium by depositing ink on the recording medium from the nozzles while moving the inkjet head relative to the recording medium.
In this type of inkjet printer, ink is supplied from an ink tank to a pressure chamber through an ink supply passage. A piezoelectric element is then driven by applying to the piezoelectric element an electric signal corresponding to image data, whereby a diaphragm constituting a part of the pressure chamber is deformed such that the volume of the pressure chamber decreases. As a result, the ink in the pressure chamber is ejected from the nozzle in liquid droplet form.
In this type of inkjet printer, a single image is formed on the recording medium by combining dots formed by the ink ejected through the nozzles.
In recent years, demands have been made of inkjet printers for high-quality image formation on a par with photographic prints. To realize such high image quality, it is possible to reduce the size of the ink droplets ejected through the nozzles by decreasing the nozzle diameter, and also to increase the number of pixels per unit area by arranging the nozzles at a higher density.
As a method of increasing the density of the nozzle array, it has been proposed that the nozzles be disposed in a two-dimensional matrix form.
For example, an apparatus is known in which a plurality of nozzles are arranged in a matrix form constituted by a plurality of rows inclined at fixed angles in relation to a head main scanning direction and a plurality of columns that are orthogonal to the head main scanning direction, and the planar form of a diaphragm which forms one surface of a pressure chamber provided for each nozzle is set in a substantially square shape or rhomboid shape. As a result, the ejection efficiency of the pressure chamber is improved, and the nozzles are disposed at a high density (see Japanese Patent Application Publication No. 2001-334661, for example).
Another apparatus is known in which a pressure chamber provided in a cavity plate is formed in a substantially rhomboid shape, an ink supply port is formed in one of the acute angle portions of the pressure chamber, and an ink ejection nozzle is formed in the other acute angle portion. As a result, a large number of ink pressure chambers corresponding to a large number of nozzles is provided without increasing the dimensions of the cavity plate, and thus the nozzles can be arranged at a high density (see Japanese Patent Application Publication No. 2002-166543, for example).
Further, Japanese Patent Application Publication No. 2001-237503 describes a thermal sheet produced with the aim of increasing heat radiation efficiency while remaining small in size, in which two sheets of conductive foil are laminated together and fixed to each other integrally. Mutually opposing linear grooves are formed in advance on the opposing surfaces of the two sheets of conductive foil by etching or laser processing so that when the two sheets are laminated together, an elongated hollow fluid channel is formed.
However, when the nozzle density is increased using inkjet head constitutions such as those described in the patent documents and so on described above, the following problems occur. Accordingly, it is difficult in reality to increase the nozzle density using these constitutions.
In an inkjet head such as those described in Japanese Patent Application Publication Nos. 2001-334661 and 2002-166543, a common ink flow passage, an ink supply passage, the pressure chamber, and the nozzle are all disposed on the same side of the diaphragm that forms one wall surface of the pressure chamber, and a piezoelectric actuator is disposed on the opposite side.
When the density of the nozzles is increased with such a constitution, the size of the common flow passage is reduced as the density increases, and hence when an attempt is made to eject ink by driving a large number of nozzles at high frequency, ink supply to the pressure chamber cannot keep up with the ink ejection.
When a common liquid chamber which supplies liquid to the pressure chamber is provided on the rear side of the diaphragm (the opposite side to the side on which the pressure chamber is provided), it is possible to increase the nozzle density, but as a result, it becomes difficult to mount drive wiring for supplying drive signals to the piezoelectric element.
More specifically, when an attempt is made to increase the nozzle density by providing the pressure chamber on one side of the diaphragm and providing the common liquid chamber on the other side, the area for mounting drive wiring on the rear side of the diaphragm or the like decreases in size, and hence it becomes difficult to mount the drive wiring in reality. Alternatively, it becomes difficult to draw out the drive wiring, with the result that it also becomes difficult to manufacture the inkjet head.
Thermosetting resin can be subjected to heat treatment easily, but when resin layers made from such a resin are laminated together to form the inkjet head, warping may occur. In an inkjet head in particular, liquid ink is used, and therefore the parts which contact the liquid must be liquid-resistant. However, when resin layers are laminated together by means of so-called build-up, gaps and the like may appear between the layers due to warping, and the ink may flow into these gaps.